We have continued our work on the construction of a bioinformatic database of protein mass spectra, which we call MassBank. MassBank is a database where evidence derived from mass spectra regarding the primary structure of a protein can be stored for use by scientists, students and engineers. In the process of constructing MassBank, we realized that the usefulness of such a resource depends on the availability of a variety of software tools and basic information, set out in an integrated resource. The resource that has been built around MassBank is called PROWL (found at the universal resource locators "http//prowl.rockefeller.edu"). At the present time, PROWL receives about >1,000,000 queries per year. This development was described in a feature article in the December 1996 issue of Analytical Chemistry.